This invention relates to improvements in valves and more particularly, but not by way of limitation, to an improved gate type valve.
A gate valve of the type disclosed is particularly suitable for gas and vacuum pipe lines where a very tight seal is required. Heretofore, gate stop valves of this type employed various mechanisms for spreading two plates, superimposed on an actuator, into sealing engagement with one or more valve seats. Those mechanisms which employed linkages had the disadvantage that the bearings of the linkage were highly loaded which resulted in excessive wear. In addition, the linkage mechanism afforded too few connection points between the plates and the actuator which resulted in insufficient support. Such linkages also result in a thicker overall valve which for many applications is unacceptable. The mechanisms which employ wedge surfaces to spread the plates suffer from excessive wear unless lubricants can be used which, of course, limits the use of the gate valve to non-vacuum applications. Various mechanisms have also used balls which move in ramps in the plates and actuator. Those balls which are free and not firmly held between the plates and actuator do not always roll together often resulting in spaces developing between the balls with uneven sealing pressure being exerted on the plates. To ensure that the balls in such an environment move together and remain evenly spaced, retainer rings are often used around the balls. Because of the thickness of the retainer ring, the expansion of the plates can only be a small fraction of the thickness of the ball which is a major design hinderance. Some U.S. Letters Patents which disclose gate stop valve structures similar to that discussed above are U.S. Pat. Nos. 776,727 (Collar), 2,676,780 (Wheatly) and 3,368,792 (Schertler).
It is therefore the primary object of the present invention to provide a novel gate stop valve which overcomes the aforementioned disadvantages of similar valves in the prior art.
It is another object of the present invention to provide a gate stop valve utilizing square rollers with radiused corners which enable all rollers to be tripped at the same time resulting in an even and large outward expansion of the plates for a given roller dimension, i.e. edge height as compared to the diameter of a ball.
It is still another object of the invention to provide a gate stop valve whose use of square rollers results in a mechanism with a mechanical advantage that is favorable in that it becomes large when sealing force is required.
It is yet another object of the present invention to provide a gate stop valve that, when the rotation of the square rollers exceeds 45.degree., the mechanism goes over center and latches which prevents unlatching due to shock and the like.
It is a still further object of the present invention to provide a gate stop valve that is relatively narrow in thickness, is quiet acting and extremely efficient in its operation and sealing capabilities.